Police have reported that the six-hour siege at a Cambodian nursery school, in which a Canadian toddler died, began as an attempt to murder two pupils in a revenge attack by their father's disgruntled former driver.

Deputy military police commander Prak Chanthoeun gave details after officers had interrogated four men captured at Siem Reap international school on Thursday.

He said that when the perpetrators could not find their targets at the school, and realised that security forces had surrounded the complex, they took about 30 other children and two teachers hostage.